* Anti-EU party on course to poll strongly in European vote
* Former party member queries leader's expenses use
* UKIP leader denies fraud, says victim of political smear
By Andrew Osborn
LONDON, April 15 (Reuters) - The leader of Britain's anti-EU UK Independence Party (UKIP) denied wrongdoing on Tuesday after a former party member referred him to the European Union's anti-fraud office less than six weeks before elections to the European Parliament.
UKIP, which wants Britain to leave the EU and an end to "open door" immigration, is forecast to poll strongly in the vote, an achievement it hopes will pave the way for it to win its first seats in the British parliament next year.
Styling itself as an antidote to the mainstream politicians it says are self-serving, the party has siphoned off support from all three main parties, and its leader, Nigel Farage, has become a regular on British television screens.
But on Tuesday, an unnamed former UKIP official queried whether Farage was using the expense allowances he gets as a member of the European Parliament (MEP) to fund one of his offices in Britain, as he says, or whether he uses it for other purposes.
The official, who sent a formal complaint about the matter to Olaf, the EU's anti-fraud office, said the running costs for his office were minimal since it was rent-free, questioning how tens of thousands of pounds earmarked for the building had actually been spent.
Farage angrily denied any wrongdoing, saying he was the victim of a "political smear" campaign. Any money he had spent had been disbursed "within the rules," he said.
"It's paid into the member's bank account and it's up to the member to spend as he or she chooses. I've used it to campaign in the United Kingdom and I've done it within the rules," he told BBC TV.
The unidentified person making the allegations against him was a convicted criminal, he added, and therefore lacked credibility.
MEPs like Farage are not required to file receipts to account for such expenditure and Olaf has not yet agreed to look into the matter and may decide not to.
Farage accused The Times, the newspaper which first published the claims, of trying to "bring down" UKIP, saying it supported Prime Minister David Cameron's Conservatives instead.
The Times is owned by Rupert Murdoch's News Corp. The media tycoon hosted a dinner for Farage in London last year but has so far declined to endorse him, despite recognising him as an effective politician.
The Times could not immediately be reached for comment.
A Guardian ICM poll published on Tuesday which asked people how they would vote in the European elections showed UKIP on 20 percent, the Conservatives on 25 percent, and Labour on 36 percent. Other polls have put UKIP ahead of the Conservatives. (Additonal reporting by William James; Editing by Robin Pomeroy)